Or, as it the series evidence of the Valiant's crewman, along with Mitchell & Dehner strongly suggests, only full humans are subject to transformation / influence of the barrier, so Spock would not be at risk.
Full humans aren't mentioned as such, so the assorted unseen casualties could have come from whichever species.
That is, the Valiant crew searches for data on human ESP specifically - but in all likelilhood, this early vessel would have had a full human crew. Or would the Valiant have been assigned a Vulcan chaperon...? But if she had one aboard, and that one got killed (either by the Barrier, or because somebody in the crew saw a convenient opening!), then again the crew would search for human data exclusively.
Kirk's casualties are not given a species identity, nor is it confirmed that all of them were espers, just that the Barrier fried a specific part of their brain. And if it does that to everybody it hits, Spock might have taken a hit but to a harmless part of his brain...
What Spock has done with his telepathy, we've seen every other Vulcan who we've seen use it do the same thing.
Except for the "The WOMEN!" thing we see in "Omega Glory"...
Timo Saloniemi